剑指offer60 n个骰子的点数【DP】

题目描述

把n个骰子扔在地上，所有骰子朝上一面的点数之和为s。输入n，打印出s的所有可能的值出现的概率。

你需要用一个浮点数数组返回答案，其中第 i 个元素代表这 n 个骰子所能掷出的点数集合中第 i 小的那个的概率。

示例 1:

输入: 1
输出: [0.16667,0.16667,0.16667,0.16667,0.16667,0.16667]

示例 2:

输入: 2
输出: [0.02778,0.05556,0.08333,0.11111,0.13889,0.16667,0.13889,0.11111,0.08333,0.05556,0.02778]

限制：

1 <= n <= 11

解题思路

方法一：动态规划

$$
f(n,x)=\sum^{6}_{1}f(n-1,x-i)✖\frac{1}{6}
$$

代码实现

class Solution60 {
    public double[] dicesProbability(int n) {
        double[] dp = new double[6];
        Arrays.fill(dp, 1.0 / 6.0);
        for (int i = 2; i <= n; i++) {
            double[] tmp = new double[5 * i + 1];
            for (int j = 0; j < dp.length; j++) {
                for (int k = 0; k < 6; k++) {
                    tmp[j + k] += dp[j] / 6.0;
                }
            }
            dp = tmp;
        }
        return dp;
    }
}

复杂度分析

时间复杂度：O($n ^ 2$)

空间复杂度：O(n)

资料

• https://leetcode-cn.com/problems/nge-tou-zi-de-dian-shu-lcof/

• https://leetcode-cn.com/problems/nge-tou-zi-de-dian-shu-lcof/solution/jian-zhi-offer-60-n-ge-tou-zi-de-dian-sh-z36d/